Black-headed budworm

Historic, Archive Document

Do not assume content reflects current
scientific knowledge, policies, or practices.

United States
Department of
Agriculture

Prepared by
Forest
Service

Alaska Region
Leaflet
R10-TP-39
August 1993

Black-Headed Budworm

The black-headed budworm is the most
significant defoliator of the coastal spruce-
hemlock forests of Alaska. This insect is
common in southwest Alaska, the Prince
William Sound area, and throughout southeast
Alaska. The black-headed budworm’s
preferred host is western hemlock, but Sitka
spruce and mountain hemlock are also
frequently fed upon.

Figure 1. Budworm defoliation along the same
Slope, 1953 (top) and 1992, Lemon Creek area,
Juneau, AK.

During budworm outbreaks, both forest and
ornamental trees are attacked.

Black-headed budworm populations in Alaska
have been cyclic, rising quickly over a few
years, covering vast areas, and then subsiding
suddenly. Recurrent infestations have been
noted in southeast Alaska since the early
1900’s (Fig. 1). An outbreak in the late 1940’s
to mid-1950’s, affected almost every forested
acre in southeast Alaska.

This leaflet provides information about the life
history of black-headed budworm and includes
several treatment options.

identification

During early development stages, budworm
larvae are creme-colored with a distinct black
head. Their body color changes to green as
they develop and the head capsule is brown
during the last development stage (Fig. 2).

Figure 2. Mature budworm larva with brown
head capsule.

Mature larvae are one-half to three-quarters
inch long. Pupae are green or brown and are
approximately one-third inch in length (Fig. 3).
The adult is a small moth with a three-quarter
inch wingspan (Fig. 4). Moths show great
variability in wing color and pattern. The
predominant wing color is grey, with mixtures of
brown, black, orange and white. Eggs are
yellow, flat, and are laid singly on the underside
of host needles (Fig. 5)

Figure 3. Black-headed budworm pupa.

Figure 4. Black-headed budworm adult (moth).
Wing color and pattern is variable.

Life history

Black-headed budworms overwinter as eggs.
The eggs hatch in late May or June and young
larvae begin feeding in unopened buds. Larval
feeding and growth coincides with the host’s
bud and shoot development. Budworm feeding
is typically confined to the current year’s
needles. Defoliation of older needles is an
indication of large budworm populations. In
their last stage of development, larvae build a
pupation shelter by webbing live and cut
needles together. Pupation occurs from mid-
July to mid-August. Moths emerge, mate, and
female moths deposit eggs from late August
through September.

Figure 5. Black-headed budworm egg on the
underside of a western hemlock needle.

Impact

Budworms are wasteful feeders, often clipping
loose needles that are not completely
consumed. By mid-summer, these needles
have dried and turn red. Crowns of heavily
defoliated trees appear scorched due to large

concentrations of dead, dry needles (Fig. 6).
Defoliation is most severe in the upper portions
of tree crowns, but entire crowns may
defoliated during budworm outbreaks.

A single year of defoliation often causes
reduced tree growth. Years of repeated |
defoliation may result in reduced cone
production, top-kill, or in severe cases, death of
the tree.

Not all impacts of budworm defoliation are
negative. Foliage ingestion hastens nutrient
cycling and crown density reduction may
increase light intensity to the ground. However,
negative impacts to managed young growth
forests and to urban ornamentals often
outweigh potential benefits.

Figure 6. Heavy defoliation of young western
hemlock and Sitka spruce.

Control

Large-scale control of the black-headed
budworm in forest settings in Alaska has not
been attempted. Control measures to protect
high value ornamentals in urban settings may

however, be desirable. Control measures for
black-headed budworm vary, based on degree
of infestation and the size and setting of
impacted trees.

No control may be necessary when budworm
populations are low and their feeding damage
is insignificant. A simple form of control for
small, lightly infested ornamentals, is to
physically remove infested shoots. Use of
insecticides may be desireable to protect
heavily infested trees. Both biological and
chemical insecticides are registered for
budworm control. Spray applications (e.g.,
carbaryl) have proven effective in reducing
budworm defoliation when applied after bud
break. A potential control method that is
currently being studied, is the use of insecticide
implants (e.g., acephate). These implants are
effective in protecting individual trees from a
similar defoliator, the western spruce budworm.
Biological insecticides (e.g., the bacterium,
Bacillus thuringiensis (B.t)), have also been
used against budworms, but proper timing of
application is critical to achieve adequate
control.

Natural controls of budworm populations vary
by budworm life stage. Predators of larvae
(and in some cases, moths) include birds,
spiders and several species of insects. Some
wasps parasitize budworm eggs, larvae and
pupae. An unusual impact to overwintering
budworm eggs is their removal by snow, as it
slides from tree branches. A virus, fungi, larval
starvation, and weather have also been noted
as having contributed to budworm population
declines.

Black-headed Budworm, by Roy A. Mask
Forest Entomologist, USDA Forest Service
Alaska Region, State and Private Forestry

August 1993

Additional information on this insect can be
obtained from your local USDA Cooperative
Extension Service office, Alaska Division of
Forestry office, or from:

USDA Forest Service

State and Private Forestry
Forest Health Management
2770 Sherwood Lane, Suite 2A
Juneau, Alaska 99801

Phone: (907) 586-8883

FAX: (907) 586-7848

CAUTION: Pesticides can be injurious to
humans, domestic animals, desirable plants,
and fish or other wildlife - if they are not
handled or applied properly. Use all pesticides
selectively and carefully. Follow recommended
practices for disposal of surplus pesticides and
their containers. Mention of a pesticide in this
publication does not constitute a
recommendation for use by the USDA, nor
does it imply registration of a product under the
Federal Insecticide, Fungicide, and Rodenticide
Act, as amended. Mention of a proprietary
product does not constitute an endorsement by
the USDA.

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